During the past year, we have continued our studies on two groups of molecules which may control the phenotype of certain normal and malignant cells. These are cell-associated protease inhibitors and low molecular weight proteins from cartilage. Because of the association of increased proteolytic activity and certain invasive phenomena, we have been characterizing a group of protease inhibitors produced by or associated with cultured cells. These include a trypsin inhibitor, a thiol protease inhibitor, a urokinase inhibitor and a collagenase inhibitor. Each of these may function individually or together to modulate the proteolytic activities of specific cell types and may, in certain instances, confer upon the cell or tissue a resistance to invasion. We have focused primarily, at this time, on the isolation and characterization of these molecules with the intent of assaying their biological activities only when we know their properties and can study them in pure form. A second area of work is fractionating certain low-molecular-weight proteins from cartilage. These molecules, some of which may be protease inhibitors, may confer upon cartilage its resistance to tumor invasion as well as its avascular state. To this end, we have been purifying a collagenase inhibitor and a thiol protease inhibitor and have set up assays for cell motility. We\have begun to explore those factors which may be involved in stimulating vascularization to define those molecules which inhibit it. Next year we plan to characterize further these inhibitors and to test their activity in several biological assays.